It is well known that pressure differentials in an air mass will cause air to flow from a point of relatively higher pressure, to a point of relatively lower pressure. Further, it is well known that this airflow is predictable when the flow path between the points is confined, such as by a duct. It cannot, however, always be assumed that a confined airflow system, such as HVAC, is not somehow compromised, or otherwise diminished in its efficiency. One way to inspect, monitor and evaluate the efficiency of an airflow system in this regard is to determine whether there are any air leaks in the ducting of the system.
In a typical HVAC system, air is circulated to and from an enclosure through a duct. Specifically, for this circulation, the duct is intended to provide a fluid pathway that is separate from the enclosure, and that extends between an inlet and an outlet. More specifically, air from the enclosure enters the duct through the inlet, and is returned to a unit in the duct (e.g. an air conditioner). Subsequently, after being conditioned or processed by the unit, the air is re-supplied to the enclosure through the outlet of the duct. Regardless what the exact nature of the unit in the duct may be (e.g. a duct fan), there is always some means in the unit that is used to move air through the duct from an inlet to an outlet. With such structure, the duct is effectively divided into a return duct (which extends from the inlet to the fan), and a supply duct (which extends from the fan to the outlet). Also, with such structure, it happens that different pressure conditions in the enclosure can be created to test the physical integrity of both the return duct and the supply duct. Specifically, this can be done by taking appropriate airflow measurements at the inlet and at the outlet of the duct.
For purposes of this disclosure, consider the duct fan is operating in an “on” condition. Airflow through the duct will then be a direct function of the duct fan's efficiency. Also, this airflow will have a value that is measurable. With this in mind, further consider the enclosure. Specifically, consider that air pressure in the enclosure can be somehow changed (e.g. by a base fan) from an ambient pressure condition to either a “positive” overpressure condition, or a “negative” under pressure condition.
With the possible pressure differentials mentioned above, first consider only the return duct (i.e. from inlet to duct fan). If there are no leaks in the return duct, the airflow measurement through the duct inlet will remain substantially constant under all pressure conditions. This is so because airflow into the duct is determined by the efficiency of the duct fan, and is possible only through the inlet. A similar consequence, for the same reasons, results for the supply duct when there are no leaks in the supply duct. The situation changes, however, when there are leaks in either the return duct, the supply duct or both.
In contrast with the no-leak condition discussed above, consider the condition where there is a leak in the return duct under an ambient pressure condition in the enclosure. In this case, with the duct fan “on”, airflow through the duct inlet will be less than it would be for a no-leak condition. This is so because additional air is being pulled into the duct through the leak. Now consider a condition wherein there is still a leak in the return duct, but a positive overpressure is created in the enclosure. This overpressure will cause the airflow into the duct inlet to increase. At the same time, because airflow through the duct fan remains substantially constant, the inflow of air through the leak will be diminished. On the other hand, when a negative under pressure is created in the enclosure, the reverse will happen. A decreased airflow through the duct inlet will cause the inflow of air through the leak to increase, in order to maintain the same duct fan airflow.
Using a similar analysis for the supply duct, it can be shown that when there is a leak in the supply duct, a predictable variation in airflow through the outlet results. As before, when it is “on”, the duct fan will establish a same airflow through the duct fan, regardless whether there is a leak in the supply duct. Under an ambient pressure condition in the enclosure, however, airflow from the outlet with a supply duct leak will be more than it would be for a no-leak condition. This happens because additional air is entering the supply duct through the leak. With a positive overpressure in the enclosure, however, airflow through the duct outlet will decrease while, at the same time, the outflow of air through the leak will increase. On the other hand, if a negative under pressure is applied in the enclosure, an increased airflow through the duct outlet will result and the outflow of air through the leak will be decreased.
In light of the above, it is an object of the present invention to provide a system and a method for determining air leakage in “real time” in a duct, while the duct is operationally in use. Another object of the present invention is to provide a system and a method for determining air leakage in a duct without physically altering the duct during the text and evaluation procedure. Still another object of the present invention is to provide a system and a method for determining air leakage in a duct that is relatively simple to manufacture, is easy to use, and is comparatively cost effective.